Steam generator

ABSTRACT

A steam generator includes: a water storage chamber which stores water therein, a heater which heats inside the water storage chamber to generate steam, a water supply device which supplies the water storage chamber with water, a steam spout port which ejects steam generated in the water storage chamber therethrough, a temperature detector which detects a temperature in the water storage chamber, and a controller which controls the heater and the water supply device, wherein after the start of the heating by the heater, the controller determines if water storage is completed in the water storage chamber based on the temperature detected by the temperature detector.

This application is a 371 application of PCT/JP2014/002165 having aninternational filing date of Apr. 16, 2014, which claims priority to JP2013-098186 filed May 8, 2013, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a steam generator for heating water togenerate steam.

BACKGROUND ART

Conventionally, this type of steam generator is to supply a second tankas a water storage chamber with a large amount of water, and then toheat the water in the second tank by energizing a heater to generatesteam if a water level detector detects a predetermined water level (forexample, see Patent Document 1).

In addition, there is other steam generator which heats a steamgenerating container by a steam heater, wherein after a temperature ofthe steam generating container detected becomes a temperature necessaryfor generating steam, the steam generator intermittently supplies waterwhich can be evaporated instantly for generating steam to the steamgenerating container (for example, see Patent Document 2).

PATENT DOCUMENTS

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-054096

Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-216803

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the configuration of Patent Document 1 includes a water leveldetector (for example, float or electrode) as a means for detecting thewater level. For example, in the case of using a float as water leveldetector, scale or the like may be deposited at the float, and the floatmay vary with foam in a water surface, thereby leading to falsedetection of the water level. Also, in the case of using an electrode aswater level detector, scale or the like may be deposited at theelectrode, and dew condensation may occurs on the electrode, therebyleading to false detection of the water level. Thus, when using suchwater level detectors, false detection of the water level is likely tooccur and in some cases, water level detection may become impossible.

The configuration of Patent Document 2 uses a temperature detectorrather than a water level detector, but the temperature detector isintended to determine whether or not the temperature of the steamgenerating container has reached a temperature for evaporating the waterinstantly. Even if the predetermined temperature is detected by thetemperature detector, only the amount of water to be evaporatedinstantly will be supplied. According to the manner, water storageamount cannot be detected accurately when a large amount of water isstored in the steam generating container. Thus, it is not possible tocontinuously generate a large amount of steam.

The present invention has been developed to solve the above-describedproblem and is intended to provide a steam generator operable togenerate steam while accurately detecting water amount in the waterstorage chamber when a large amount of water is stored in the waterstorage chamber without using water level detector which is likely tocause false detection.

Means to Solve the Problems

In solving the above-described problem, a steam generator of the presentinvention includes: a water storage chamber which stores water therein,a heater which heats inside the water storage chamber to generate steam,a water supply device which supplies the water storage chamber withwater, a steam spout port which ejects steam generated in the waterstorage chamber therethrough, a temperature detector which detects atemperature in the water storage chamber, and a controller whichcontrols the heater and the water supply device, wherein after the startof the heating by the heater, the controller determines if water storageis completed in the water storage chamber based on the temperaturedetected by the temperature detector.

Effects of the Invention

The steam generator according to the present invention can generatesteam while accurately detecting water amount in the water storagechamber when a large amount of water is stored in the water storagechamber without using water level detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and features of the present invention will becomeapparent from the following description of a preferred embodimentthereof with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a heating cooker provided with a steamgenerator according to a first embodiment of the present invention witha door opened;

FIG. 2 is a perspective view of the heating cooker provided with thesteam generator according to the first embodiment as viewed from a steamgenerator side with an outer casing omitted;

FIG. 3 is a front cross-sectional view of the heating cooker providedwith the steam generator according to the first embodiment with theouter casing omitted;

FIG. 4A is a side cross-sectional view of the steam generator accordingto the first embodiment;

FIG. 4B is another side cross-sectional view of the steam generatoraccording to the first embodiment;

FIG. 5 is a side view of the heating cooker according to the firstembodiment as viewed from the steam generator side;

FIG. 6 is a front view of a water storage chamber according to the firstembodiment;

FIG. 7A is a perspective view of the water storage chamber according tothe first embodiment;

FIG. 7B is another perspective view of the water storage chamberaccording to the first embodiment;

FIG. 8 is a horizontal cross-sectional view of the steam generatoraccording to the first embodiment;

FIG. 9 is a flowchart of a steam heating mode of the steam generatoraccording to the first embodiment;

FIG. 10A is a graph indicating a relationship between the temperature ofthe water storage chamber thermistor and time in the steam generatoraccording to the first embodiment;

FIG. 10B is a graph indicating a relationship between the temperature ofthe water storage chamber thermistor and time in the steam generatoraccording to the first embodiment;

FIG. 10C is a graph indicating a relationship between the temperature ofthe water storage chamber thermistor and time in the steam generatoraccording to the first embodiment;

FIG. 11A is a first cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting a waterdischarge process according to the siphon principle;

FIG. 11B is a second cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process according to the siphon principle;

FIG. 11C is a third cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process according to the siphon principle;

FIG. 11D is a fourth cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process according to the siphon principle;

FIG. 12A is a first cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting a waterdischarge process in a water supply passage;

FIG. 12B is a second cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process in the water supply passage;

FIG. 12C is a third cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process in the water supply passage; and

FIG. 12D is a fourth cross-sectional view of the steam generatoraccording to the first embodiment, schematically depicting the waterdischarge process in the water supply passage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first invention is a steam generator including: a water storagechamber which stores water therein, a heater which heats inside thewater storage chamber to generate steam, a water supply device whichsupplies the water storage chamber with water, a steam spout port whichejects steam generated in the water storage chamber therethrough, atemperature detector which detects a temperature in the water storagechamber, and a controller which controls the heater and the water supplydevice, wherein after the start of the heating by the heater, thecontroller determines if water storage is completed in the water storagechamber based on the temperature detected by the temperature detector.The steam generator uses a temperature detector which detects atemperature in the water storage chamber not using a water leveldetector, thereby generating steam while accurately detecting wateramount in the water storage chamber if a large amount of water is storedin the water storage chamber.

A second invention is a steam generator according to the firstinvention, wherein after the start of the heating by the heater, thecontroller starts the water supply by the water supply device when thetemperature of the water storage chamber detected by the temperaturedetector becomes equal to or higher than a first predeterminedtemperature, and determines if the water storage in the water storagechamber is completed based on the temperature in the water storagechamber after the start of the water supply. Such control is to startthe water supply with estimating that the water amount in the waterstorage chamber becomes small when the temperature of the water storagechamber becomes equal to or higher than the first predeterminedtemperature. Thus, the steam generator can generate steam whileaccurately detecting the water amount in the water storage chamber usingthe temperature detector.

A third invention is the steam generator according to the secondinvention, wherein after the water supply, the controller determinesthat the water storage in the water storage chamber is completed whenthe temperature in the water storage chamber becomes equal to or lowerthan a second predetermined temperature. Such control is to determinecompletion of the water storage with estimating that the water storageamount is increased to a predetermined storage amount when thetemperature of the water storage chamber becomes equal to or lower thana second predetermined temperature. Thus, the steam generator cangenerate steam while accurately detecting the water amount in the waterstorage chamber using the temperature detector. Also, the steamgenerator can prevent overflow of the water from the water storagechamber due to excess water supply or prevent slow steam generation dueto insufficient water supply.

A fourth invention is the steam generator according to the secondinvention or the third invention, wherein after the water supply by thewater supply device, the controller determines that the water storage inthe water storage chamber is completed when the temperature in the waterstorage chamber is decreased by equal to or more than a firsttemperature width from the start of the decrease. Such control is toestimate that the water storage amount in the water storage chamberbecomes equal to or larger than a predetermined amount when thetemperature in the water storage chamber is decreased by equal to orhigher than the first temperature width (for example, 20° C.) from thestart of the decrease after the water supply, in particular, in a casewhere an initial amount in the water storage chamber is small. Thus, thesteam generator can generate steam while accurately detecting the wateramount in the water storage chamber using the temperature detector.Also, the steam generator can prevent overflow of the water from thewater storage chamber due to excess water supply or prevent slow steamgeneration due to insufficient water supply.

A fifth invention is the steam generator according to any one of thefirst invention to the fourth invention, wherein after the start of theheating by the heater, the controller determines that the water storagein the water storage chamber has been completed when a temperaturechange of the water storage chamber detected by the temperature detectoris within a second temperature width in a predetermined period, and thencontrols the water supply device not to supply the water. Such controlis to estimate that the water level in the water storage chamber issufficiently high by the fact that the temperature change of the waterstorage chamber detected by the temperature detector is within thepredetermined temperature width in the predetermined period. Thus, thesteam generator can generate steam while accurately detecting the wateramount in the water storage chamber using the temperature detector.Also, the steam generator can prevent overflow of the water from thewater storage chamber due to excess water supply or prevent slow steamgeneration due to insufficient water supply.

A sixth invention is the steam generator according to any one of thefirst invention to the fifth invention, wherein the controller controlsthe water supply device to supply the water intermittently. Such controlcan control the water supply amount more accurately.

A seventh invention is the steam generator according to the sixthinvention, wherein the controller determines that the water storage inthe water storage chamber is completed when a number of the water supplyby the water supply device reaches a predetermined number. Such controlcan complete water storage with sufficient amount of water even if thewater supply is started when no water is initially stored in the waterstorage chamber. Also, overflow of the water from the water storagechamber due to excess water supply can be prevented.

An eighth invention is a heating cooker provided with the steamgenerator according to any one of the first invention to the seventhinvention.

An embodiment of the present invention is described hereinafter withreference to the drawings, but the present invention is not limited bythe embodiment.

Embodiment 1

FIG. 1 is a perspective view of a heating cooker provided with a steamgenerator according to a first embodiment of the present invention. FIG.1 depicts a state where a door of the heating cooker has been opened.

In FIG. 1, the heating cooker 1 is provided with a housing 4. Thehousing 4 is a cuboidal housing having a heating chamber opening 3defined in a front surface 2. The housing 4 is provided with an innercasing 5 and an outer casing 6. The inner casing 5 is a box having aheating chamber 10 defined therein. The inner casing 5 is formed of analuminum-plated steel plate coated with fluorine. The outer casing 6 isa PCM steel plate that covers the inner casing 5. A food tray 9 and afood 11 can be taken in or out of the heating chamber 10 through theheating chamber opening 3. In the heating chamber 10, the food tray 9with the food 11 placed thereon can slide on rails 12 of the innercasing 5. Although in the first embodiment the inner casing 5 is coatedwith fluorine for ease of wiping off dirt adhering to the inner casing5, the coating is not limited thereto and may be a porcelain enamelcoating or other heat-resistant coatings. Also, the inner casing 5 ismade of, for example, stainless steel.

The food tray 9 is formed of an aluminum-plated steel plate and into aconcavo-convex shape by press working so that oil and fat contents mayeasily flow out of the food 11 when the food 11 placed on the food tray9 is heated. The food tray 9 is coated with fluorine and has a heatingelement mounted on a rear surface thereof to generate heat by absorbingmicrowaves. Providing the heating element on the rear surface of thefood tray 9 can heat the food 11 from both sides by a combination of aheating chamber heater 15 located above the food tray 9 (see FIG. 3) andthe heating element mounted on the rear surface of the food tray 9. Thefood tray 9 has rail abutments 13 secured to a lower portion thereof.The rail abutments 13 are located at contact portions of the food tray 9with the rails 12 and screwed to the lower portion of the food tray 9.The rail abutments 13 are each formed of a PPS resin molding to insulatethe food tray 9 from the heating chamber 10.

Although in the first embodiment the surface of the food tray 9 has beendescribed as being coated with fluorine for ease of wiping dirt off, aporcelain enamel coating or any other heat-resistant coating may beapplied thereto. Also, the material of the food tray 9 may be aluminumor stainless steel.

A door 7 is mounted on the front surface 3 of the housing 4 so as to berotatable (openable and closable) about a horizontal axis. When the door7 is rotated toward a vertical position (the door 7 is opened), theheating chamber 10 is closed. When the door 7 is rotated toward ahorizontal position (the door 7 is closed), the heating chamber 10 isopened. A safety switch 8 is mounted on the front surface 3 of thehousing 4 to stop operation of a magnetron and each heater when the door7 is opened.

FIG. 2 is a perspective view of the heating cooker 1 according to thefirst embodiment with the outer casing 6 omitted. In FIG. 2, a steamgenerator 27 is illustrated as being exposed.

In FIG. 2, a touch panel 57 and an operating portion 58 are provided onthe door 7. The touch panel 57 includes a screen accessible to a user.The user touches the screen of the touch panel 57 with a finger to setthe cooking menu and cooking time in detail. The user operates theoperating portion 58 to carry out basic operations such as “return”,“cancel” and “start”. Although in the first embodiment the touch panel57 is provided, a mere liquid crystal display may be employed in placeof the touch panel 57. If the liquid crystal display is employed inplace of the touch panel 57, the user may select the cooking menu andcooking time displayed on the liquid crystal display using arrow keys ora dial key provided on the operating portion 58.

FIG. 3 is a front cross-sectional view of the heating cooker 1 accordingto the first embodiment with the outer casing 6 omitted.

As shown in FIG. 3, the heating cooker 1 is provided with a food table14 and heating chamber heaters 15. The food table 14 is a table forplacing a food thereon and is secured to the heating chamber 10 toconstitute a bottom surface of the heating chamber 10. The food table 14is formed of crystallized glass. The heating chamber heaters 15 arethree heaters disposed parallel to one another and adjacent to an uppersurface of the heating chamber 10. Of the three heating chamber heaters15, the heating chamber heater 15 located at a central portion has apeak wavelength value shorter than peak wavelength values of the othertwo heating chamber heaters 15.

Wall surfaces of the heat chamber 10 are grounded by means of an earthcable (not shown) and the rails 12 integrally formed with the heatingchamber 10 are also grounded.

A circulation fan 16 and a convection heater 17 are provided on a rearside, that is, at the back of the heating chamber 10. The circulationfan 16 is a fan for stirring and circulating air within the heatingchamber 10. The convection heater 17 is an interior air-heating heaterfor heating air that circulates within the heating chamber 10 and isprovided so as to encircle the circulation fan 16.

A plurality of intake vent holes 18 and a plurality of blow vent holes19 are formed at different areas adjacent to the center of a rear wallof the heating chamber 10. The intake vent holes 18 are holes fordrawing air from the heating chamber 10 side to the circulation fan 16side. In contrast, the blow vent holes 19 are holes for blowing air fromthe circulation fan 16 side to the heating chamber 10 side. The intakevent holes 18 and the blow vent holes 19 are formed by a plurality ofpunch holes.

In FIG. 3, an infrared sensor 21 and an inside thermistor 22 areprovided at an upper right portion of the heating chamber 10. Theinfrared sensor 21 detects the temperature of a food within the heatingchamber 10 through a detection hole 20 defined in a wall of the heatingchamber 10. The inside thermistor 22 detects the temperature (internaltemperature) of the heating chamber 10.

In FIG. 3, a magnetron 23, a waveguide 24, a rotating antenna 25 and amotor 26 are provided below the heating chamber 10. The magnetron 23 isan example of a microwave generating unit for generating microwaves. Themagnetron 23 has a shape of 80 mm×80 mm as viewed from the left andextends horizontally. The magnetron 23 is connected to the waveguide 24.The waveguide 24 is a pipe for transmitting the microwaves from themagnetron 23 and has an internal channel formed by bending analuminum-plated steel plate into approximately an L shape. The rotatingantenna 25 is an example of a microwave stirring means disposed adjacentto a horizontal center of the heating chamber 10. The rotating antenna25 is formed of aluminum and connected to the motor 26.

Although in the first embodiment the magnetron 23, the rotating antenna25, the motor 26 and the waveguide 24 have been described as beingprovided below the heating chamber 10, the present invention is notlimited to such a configuration. For example, these components can beprovided on an upper or lateral side of the heating chamber 10. Also,orientations of these components can be arbitrarily determined. Therotating antenna 25 and the motor 26 are not always required.

In the first embodiment, a controller 34 is provided below the waveguide24. The controller 34 controls, based on the cooking menu selected bythe user, the magnetron 23, the motor 26, the circulation fan 16, theheating chamber heaters 15, a first steam generating heater 50, a secondsteam generating heater 51, the convection heater 17, the insidethermistor 22, a water storage chamber thermistor 33, the infraredsensor 21, a water supply pump 41, the touch panel 57, the operatingportion 58 and the like.

The steam generator 27 is located on the left side of the heatingchamber 10. The steam generator 27 is provided with a water storagechamber 28, a water storage chamber packing 29, a water storage chambercover 30, a steam passage 31 and a steam spout port 32. The waterstorage chamber 28 is a container for storing water therein for steamgeneration and is formed by aluminum die-casting. The water storagechamber cover 30 is disposed so as to confront the water storage chamber28 and mounted on the water storage chamber 28 via the water storagechamber packing 29 made of silicone. The water storage chamber cover 30is located more closely to the heating chamber 10 than the water storagechamber 28 and formed by aluminum die-casting. The water storage chamber28 and the water storage chamber cover 30 may be collectively referredto as the “water storage chamber”. The steam passage 31 is a pipeconnected to the water storage chamber 28 at an upper portion thereof tosupply steam to the heating chamber 10 from an upper portion of a sidesurface of the heating chamber 10. The steam passage 31 is formed by asilicone tube having an inner diameter of 10 mm. The steam spout port 32is connected to the steam passage 31 to eject steam into the heatingchamber 10 from the side surface of the heating chamber 10 above theupmost rails 12. That is, the steam generated within the water storagechamber 28 is ejected into the heating chamber 10 through the steamspout port 32. A member which forms the steam spout port 32 is formed ofa PPS resin.

The steam spout port 32 extends from the steam passage 31 toward theheating chamber 10 so as to incline obliquely downward at an angle ofabout 30 degrees from the horizontal direction and is connected to arecessed surface of the heating chamber 10. A distal end of the steamspout port 32 does not protrude into the heating chamber 10 from theside surface of the heating chamber 10. The member forming the steamspout port 32 also has two U-shaped notches defined in a distal endportion thereof. In the first embodiment, the steam spout port 32inclines obliquely downward at the angle of about 30 degrees from thehorizontal direction, but the angle is not limited to 30 degrees.

Also, in the first embodiment, each of the steam passage 31 and thesteam spout port 32 has a round cross-sectional shape, but it may havean ellipsoidal or rectangular cross-sectional shape. One steam spoutport 32 is provided at the upper portion of the side surface of theheating chamber 10, but the position and number of the steam spout port32 are not limited thereto. The steam spout port 32 may be locatedanywhere, for example, in an upper surface, a bottom surface or a rearsurface of the heating chamber 10, so long as the heating chamber 10 canbe supplied with steam. Also, a plurality of steam spout ports may beprovided in place of the one steam spout port 32. The position of thesteam generator 27 is not limited to on a lateral side of the heatingchamber 10 and may be on an upper side, a lower side or a rear side ofthe heating chamber 10.

It is preferable that a maximum inner dimension of the steam spout port32 be not greater than half a wavelength of microwaves so that themicrowaves within the heating chamber 10 may not leak from the steamspout port 32. In the first embodiment, the wavelength of microwaves isabout 120 mm, so it is preferable that the maximum inner dimension ofthe steam spout port 32 be not greater than 60 mm.

FIG. 4A is a side cross-sectional view depicting an entire configurationof the steam generator 27 according to the first embodiment and FIG. 4Bis an enlarged view of a main section of the steam generator 27according to the first embodiment.

As shown in FIG. 4A and FIG. 4B, the steam generator 27 is provided witha first steam generating heater 50 and a second steam generating heater51. The first steam generating heater 50 is an example first heatingportion for heating water stored in the water storage chamber 28 togenerate steam and composed of a linear sheathed heater having an outputof 650 W. The first steam generating heater 50 has been casted in analuminum die-cast of the water storage chamber 28 so as to extendsubstantially horizontally at a location adjacent to a vertical centerof the water storage chamber 28. The second steam generating heater 51is an example second heating portion for heating water stored in thewater storage chamber 28 to generate steam and composed of a linearsheathed heater having an output of 350 W. The second steam generatingheater 51 extends substantially horizontally above the first steamgenerating heater 50. As with the first steam generating heater 50, thesecond steam generating heater 51 has been casted in the aluminumdie-cast of the water storage chamber 28. The heating portions may be anIH type other than a heater, for example.

The distance between a first side surface 53 and a second side surface54 confronting each other in the water storage chamber 28 becomesgreater below the first steam generating heater 50 (L1>L2). That is, thedistance between the water storage chamber 28 and the water storagechamber cover 30 is greater at a location of a water storage chamberrecess 28 a located below the first steam generating heater 50 than at alocation adjacent to the first steam generating heater 50 and the secondsteam generating heater 51, and a sectional area of the former locationis also greater than that of the latter location. A recess 30 a isformed in an inner wall of the water storage chamber cover 30 at alocation facing the first steam generating heater 50. That is, the waterstorage chamber cover 30 has the recess 30 a formed therein at thelocation facing the first steam generating heater 50 to be concentricwith the first steam generating heater 50 and to expand rightward.

A water storage chamber thermistor 33 is provided between the firststeam generating heater 50 and the second steam generating heater 51.The water storage chamber thermistor 33 is an example temperaturedetector for detecting the temperature of the water storage chamber 28.The water storage chamber thermistor 33 is coated with athermally-conductive grease and held in contact with the water storagechamber 28.

In the first embodiment, two linear sheathed heaters having differentoutputs are used as the first steam generating heater 50 and the secondsteam generating heater 51 to have a total output of 1000 W (650 W onthe lower side and 350 W on the upper side). The present invention isnot limited to such a configuration, and one or more heaters having adesired output may be adopted depending on, for example, amount of steamrequired. For example, a plurality of heaters having a different totaloutput from 1000 W or each having the same output can be used. Usingthree or more heaters or only one heater is also possible. Further,heaters having various shapes other than the linear heaters can be used.For example, using U-shaped or L-shaped heaters is also possible. Inaddition, the output of the upper heater may be greater than that of thelower heater.

Although in the first embodiment the recess 30 a in the water storagechamber cover 30 has been described as expanding rightward andconcentrically with the first steam generating heater 50, the presentinvention is not limited to such a case. For example, the water storagechamber cover 30 may have a recess in the form of a similar shape at alocation confronting the second steam generating heater 51 or any otherheater, thereby producing the same effects as the recess 30 a.

Also, in order to reduce adherence of scales, an inner surface of thewater storage chamber 28 or the water storage chamber cover 30 may becoated with fluorine, silicone or the like.

Contrary to a water level detecting member such as a float for directlydetecting the water level, using a temperature detector such as thewater storage chamber thermistor 33 can continuously detect thetemperature for a long period of time even if scales adhere to thedetector, thereby enhancing reliability against scales.

FIG. 5 is a side view of the heating cooker 1 having the steam generator27 according to the first embodiment as viewed from the steam generator27 side.

As shown in FIG. 5, the steam passage 31 extends upward from a centralportion of the steam generator 27 and is bent substantially in thehorizontal direction (rightward in FIG. 5). Two temperature switches 60are provided to the upper left of the steam generator 27. Thetemperature switches 60 are switches that are deactivated when thetemperature reaches 135° C. The temperature switches 60 are screwed tothe water storage chamber 28 via respective aluminum plates having athickness of 1 mm. A water supply port 38, a water supply passage 40, awater supply pump 41 and a water supply tank 42 are provided to thelower left of the water storage chamber 28. The water supply passage 40is a pipe disposed on an upstream side of the water supply port 38 andformed of a translucent elastic silicone body. The water supply passage40 has an inner diameter of 3 mm and an outer diameter of 5 mm. Thewater supply pump 41 is a pump for supplying water. The water supplytank 42 is a tank for storing water therein, which is to be suppliedfrom the water supply pump 41 to the water storage chamber 28. As justdescribed, the water supply pump 41 is provided as a water supply devicefor supplying water through the water supply passage 40 and the watersupply port 38 formed in the water storage chamber 28.

On the other hand, a water discharge port 39, a water discharge passage43, a water discharge passage outlet 46 and a water discharge tank 47are provided to the lower right of the water storage chamber 28. Thewater discharge passage 43 is a pipe connected to the water dischargeport 39 and formed of a translucent elastic silicone body having aninner diameter of 7 mm and an outer diameter of 11 mm. The waterdischarge passage 43 extends rightward from the water discharge port 39substantially in the horizontal direction and is bent vertically beforeit further extends so as to incline to the upper right to some extent.The water discharge passage 43 is further bent at an angle of 180degrees by a tube bending member 61 with an upmost point 44 thereof asan apex before it extends downward substantially in the verticaldirection. The apex 44 of the water discharge passage 43 is locatedsubstantially at the same level as a steam spout port 45 formed abovethe water storage chamber 28. Then, the water discharge passage 43extends so as to incline to the lower right to some extent and isconnected to the water discharge passage outlet 46 (having an innerdiameter of 8 mm) substantially at the same level as the water dischargeport 39. The water discharge tank 47 for storing drainage water thereinis provided below the water discharge passage outlet 46. As justdescribed, the water discharge passage 43 is provided to discharge waterin the water storage tank 28 through the water discharge port 39provided in the water discharge chamber 28.

In this embodiment, the water discharge passage 43 is formed ofsilicone, but the material is not limited to silicone and the waterdischarge passage 43 may be formed of, for example, fluorine,polypropylene or polyethylene.

The water supply tank 42 is made up of two components, i.e., a containerportion and a lid portion, and each of them is formed of a transparentAS resin. The container portion and the lid portion are hermeticallyclosed by a packing (not shown) sandwiched therebetween to avoid waterleakage. A water discharge line 49 and a full water line 52 areindicated on a side surface of the water supply tank 42 by silk screenprinting. When the water supply tank 42 is supplied with water to alevel indicated by the water discharge line 49, the water volume storedin the water supply tank 42 becomes about 100 ml, which is 10 ml greaterthan an inner volume of the water storage chamber 28. When the watersupply tank 42 is supplied with water to a level indicated by the fullwater line 52, the water volume stored in the water supply tank 42becomes about 650 ml.

The water discharge tank 47 is formed of an ABS resin as one componentof the container portion. The heating cooker 1 is provided with a waterdischarge tank detector (not shown). Using the water discharge tankdetector allows a user to recognize whether or not the water dischargetank 47 has been mounted on the heating cooker 1.

Although in the first embodiment the water discharge line 49 and thefull water line 52 have been described as being indicated by silk screenprinting, the indication method is not limited to the silk screenprinting. For example, those lines may be engraved on the water supplytank 42 or indicated by a concave or convex portion formed on the watersupply tank 42.

FIG. 6 is a front view of the water storage chamber 28 of the steamgenerator 27 according to the first embodiment. FIG. 7A and FIG. 7B areperspective views of the water storage chamber 28 of the steam generator27 according to the first embodiment. FIG. 7A is a perspective view ofthe water storage chamber 28 of the steam generator 27 according to thefirst embodiment as viewed from the lower right and FIG. 7B is aperspective view of the water storage chamber 28 of the steam generator27 according to the first embodiment as viewed from the lower left.

As shown in FIG. 6, the water storage chamber 28 is provided with apartition plate 56 and a plurality of fins 36. The partition plate 56 isa plate for preventing water in the water storage chamber 28 fromboiling over the water storage chamber 28. The partition plate 56 has agenerally circular arc shape and an apex positioned at an upper portionof the center of the water storage chamber 28. The plurality of fins 36are integrally formed with an inner wall of the water storage chamber 28and having a thickness of about 2 mm. A longitudinal direction of thefins 36 extends so as to substantially perpendicularly cross the firststeam generating heater 50 and the second steam generating heater 51.The plurality of fins 36 are formed along a steam-generating direction,in which steam is generated (a direction from bottom to top in FIG. 6),and positioned apart from one another. Of the plurality of fins 36, thefins 36 positioned at a central portion of the water storage chamber 28(within a first range “e1”) are horizontally aligned at a first interval“d1” (about 5 mm), but the fins 36 positioned on right and left endsides (within second ranges “e2”) are horizontally aligned at a secondinterval “d2” (about 12 mm). The ratio of the first range e1 to thesecond ranges e2×2 is set to 5:6. Specifically, the first range e1 is 50mm and each of the second ranges e2 is 30 mm. Of the plurality of fins36, fins 36 c, 36 d positioned at the central portion of the waterstorage chamber 28 are connected to a mounting portion of the waterstorage chamber thermistor 33.

Thicknesses, lengths and intervals of the fins 36 are not limited to theabove-described values and may be appropriately determined in the lightof the thermal conductivity of the fins 36. For example, thethicknesses, lengths and intervals of the fins 36 may be appropriatelydetermined in the light of the shape of the water storage chamber 28,the configuration of the first steam generating heater 50 and the secondsteam generating heater 51, or the like.

An inner bottom surface 37 of the water storage chamber 28 is formedinto a tapered shape at an angle of about 5 degrees with respect to ahorizontal plane. The water supply port 38 is provided to the upperright of the inner bottom surface 37 and at a lower right end of thewater storage chamber 28. The water discharge port 39 is provided to thelower left of the inner bottom surface 37 and at a lower left end of thewater storage chamber 28. The water supply port 38 and the waterdischarge port 39 are positioned separately and extend in oppositedirections. The inner bottom surface 37 is inclined downward from thewater supply port 38 toward the water discharge port 39.

Although in the first embodiment the inner bottom surface 37 has beendescribed as being tapered at an angle of about 5 degrees with respectto a horizontal plane, the angle is not limited thereto. Water flow onthe inner bottom surface 37 depends on the angle of the inner bottomsurface 37, and thus the angle may be appropriately determined in thelight of the shape of the water storage chamber 28, the shape of thewater discharge passage 43, the amount of water supply at the time ofdrainage, or the like. Also, the inner bottom surface 37 may extendparallel to a horizontal plane and/or may not be straight.

A rib 55 is provided at lower ends of the fins 36 below the first steamgenerating heater 50. The rib 55 is integrally formed with the waterstorage chamber 28 so as to connect an inner side wall 28A of the waterstorage chamber 28 with the fins 36 and to extend parallel to the innerbottom surface 37. The rib 55 has a thickness of about 2 mm. The rib 55connects the plurality of fins 36 together at the lower ends of the fins36. The rib 55 and the inner bottom surface 37 forms an inner flowchannel for communicating the water discharge port 39 with the watersupply port 38

Although the rib 55 is provided at the lower ends of the fins 36, theposition of the rib 55 is not limited thereto and may be anywhereupstream of the water discharge port 39. For example, the rib 55 may beprovided anywhere on the fins 36 as long as the rib 55 can connect theinner side wall 28A of the water storage chamber 28 with the fins 36.Also, the rib 55 is provided parallel to the inner bottom surface 37,but does not have to be parallel to the inner bottom surface 37 and mayextend horizontally or along a curved line. Further, the fins 36 areconnected to the rib 55, but they do not have to be connected completelywith each other and may be disposed with a minute gap interposedtherebetween.

FIG. 8 is a horizontal cross-sectional view of the steam generator 27according to the first embodiment.

As shown in FIG. 8, the fins 36 are formed so as to protrude from afirst side surface 53 of the water storage chamber 28. The fins 36 haverespective side edges 36A spaced from a second side surface 54 of thewater storage chamber cover 30 that faces the first side surface 53 (seethe side cross-sectional view of FIG. 4B). Gaps between the side edges36A of the fins 36 and the second side surface 54 are about 2 mm. On theother hand, side edges 36B of the fins 36 adjacent to the rib 55 arepositioned substantially in contact with the second side surface 54. Agap between the rib 55 and the second side surface 54 is about 5 mm(FIG. 8).

The rib 55 has a plurality of openings 59 each formed by a recess 55A.The openings 59 are formed by the fins 36, the recesses 55A in the rib55 and the second surface 54 and have a generally rectangularcross-sectional shape, respectively. The length of diagonal lines of thegenerally rectangular shapes of the openings 59 is smaller than an inlet39 a of the water discharge port 39 as shown in FIG. 7A. That is, theopenings 59 are positioned upstream of the water discharge port 39 andhave a size smaller than the inlet 39A of the water discharge port 39.

The fins 36 and the rib 55 gradually become thin at an inclination angleof about 2 degrees as they approach the second side surface 54 from thefirst side surface 53. The cross-sectional area of each of a pluralityof spaces delimited by the first side surface 53, the second sidesurface 54 and the fins 36 is not smaller than that of the steam spoutport 32.

Although in the first embodiment the side edges 36A of the fins 36formed so as to protrude from the water storage chamber 28 are spacedabout 2 mm from the second side surface 54 of the water storage chambercover 30, the size of the gaps is not limited thereto. The gaps betweenthe side edges 36A of the fins 36 and the second side surface 54 may beappropriately determined as long as the gaps allow water to pass betweenthe fins 36 and the water storage chamber cover 30.

The operation and function of the heating cooker 1 having the steamgenerator 27 of the above-described configuration are explainedhereinafter.

When a user selects a microwave heating mode using the touch panel 57and pushes a start button of the operating portion 58, the magnetron 23emits microwaves. The microwaves emitted from the magnetron 23 passthrough the waveguide 24 and are directed to the rotational antenna 25.Then, the microwaves are supplied to the inside of the heating chamber10 while being stirred by the rotational antenna 11 that is rotated bythe motor 26. Some of the microwaves supplied to the heating chamber 10are directly absorbed by a food 11 which is an object to be heated, andsome of them are absorbed by the food 11 to heat the food 11 afterreflected by wall surfaces of the heating chamber 10. Some of themicrowaves return to the magnetron 23. Also, at the time of automaticheating, mainly the infrared sensor 15 and the inside thermistor 9detect the condition of the food and the condition inside the heatingchamber 10, respectively, and the controller 34 controls an output andan emitting direction of the microwaves depending on the detectedconditions. In the microwave heating mode, the food tray 9 has beenremoved from the inside of the heating chamber 10, and the food 11 isplaced on the food table 14 for subsequent heating.

When the user selects an oven heating mode using the touch panel 57 andpushes the start button of the operating portion 58, the heating chamberheater 15 or the convection heater 17 is energized to generate heat, andheated air is circulated in the heating chamber 10 by the circulationfan 16 to heat the food 11. Also, at the time of automatic heating,mainly the infrared sensor 21 and the inside thermistor 22 detect thecondition of the food and the condition inside the heating chamber 10,respectively, and the controller 34 controls switching of the heatingchamber heater 15, the convection heater 17 and the circulation fan 16or conducts an output control depending on the detected conditions.

When the user places the food tray 9 in the heating chamber 10, selectsa grill heating mode using the touch panel 57, and pushes the startbutton of the operating portion 58, microwaves are supplied to theheating chamber 10, as in the microwave heating mode, to cause theheating element mounted on the rear surface of the food tray 9 togenerate heat. The heat generated by the heating element is transferredto the food tray 9 by heat conduction to heat the food tray 9, therebyheating the food 11 from below.

At the same time, the microwaves flow through spaces between the foodtray 9 and the wall surfaces of the heating chamber 10 to heat the food11. In the grill heating mode, the heating chamber heater 15 isenergized solely or in combination with the microwaves to generate heat,and the food 11 is heated from above by radiation heat from the heatingchamber heater 15.

Also, at the time of automatic heating, mainly the infrared sensor 21and the inside thermistor 22 detect the condition of the food and thecondition inside the heating chamber 10, respectively, and thecontroller 34 controls switching between the microwaves and the heatingchamber heater 15 or conducts an output control depending on thedetected conditions. In this way, the food 11 is heated from both sides.

FIG. 9 is a flowchart of a steam heating mode of the steam generator 27according to the first embodiment. FIG. 10A-10C are graphs indicating arelationship between time and the temperature of the water storagechamber thermistor 33 provided in the steam generator 27 according tothe first embodiment. FIG. 10A shows an example in which the initialwater level in the water storage chamber 28 is high level (the initialwater storage amount is large). FIG. 10B shows an example in which theinitial water level in the water storage chamber 28 is medium level (theinitial water storage amount is neither large nor small). FIG. 10C showsan example in which the initial water level in the water storage chamber28 is low level (the initial water storage amount is small).

Firstly, a user selects the steam heating mode using the touch panel 57and pushes the start button of the operating portion 58 after refillingthe water supply tank 42 with water to a level indicated by the fullwater line 52 (step S10). Then, the controller 34 operates (turns on)the first steam generating heater 50 and the second steam generatingheater 51 to generate heat (step S11). With this operation, thecontroller 34 starts the temperature detection of the water storagechamber 28 using the water storage chamber thermistor 33 to continuouslydetect the temperature of the water storage chamber 28.

Next, it is determined whether or not a temperature change of the waterstorage chamber 28 detected by the water storage chamber thermistor 33is within ±1° C. in 10 seconds (S12). If the temperature change iswithin ±1° C., it is estimated that the water storage chamber 28 hasstored a sufficient amount of water from the start, determining that thewater storage has been completed (S19). In this case, water supply isnot performed before it is determined that the water storage has beencompleted. FIG. 10A shows an example in which it is determined at S12that the temperature change is within ±1° C., and then it is determinedat S19 that the water storage has been completed.

If it is determined at S12 that the temperature change does not fallwithin ±1° C., the controller 34 then determines if the temperature ofthe water storage chamber 28 is equal to or less than 110° C. (S13). Ifit is determined at S13 that the temperature of the water storagechamber 28 is equal to or less than 110° C., then the process returns toS12. On the contrary, when it is determined at S13 that the temperatureof the water storage chamber 28 exceeds 110° C., the controller 34issues a water supply instruction to the water supply pump 41 foroperating the water supply pump 41 to perform water supply for 1.5seconds (S14). Thus, water of about 9 ml in the water supply tank 42 issupplied to the water storage chamber 28 from the water supply pump 41via the water supply passage 40 and the water supply port 38.

Then, 5-second masking time for determining water supply is provided(S15). More specifically, a waiting time without performing water supplyis provided for 5 seconds after S14.

Next, the controller 34 determines if the temperature of the waterstorage chamber 28 is equal to or less than 110° C. (S16). Morespecifically, upon the masking time by S15 after the start of the watersupply, it is determined whether or not the temperature of the waterstorage chamber 28 becomes equal to or less than a predeterminedtemperature (110° C.). When it is determined at S16 that the temperatureof the water storage chamber 28 is equal to or less than 110° C., thecontroller 34 estimates that a predetermined amount of water is storedin the water storage chamber 28, determining that the water storage inthe water storage chamber has been completed (S19). FIG. 10B shows anexample of such a case.

Meanwhile, when it is determined at S16 that the temperature of thewater storage chamber 28 exceeds 110° C., the controller 34 determinesif the temperature of the water storage chamber 28 is changed(increased/decreased) by equal to or higher than 20° C. from the maximumtemperature value (S17). More specifically, it is determined whether ornot the temperature decreasing width is equal to or more than apredetermined temperature width (20° C. in the first embodiment) fromthe start of the temperature decrease in the water storage chamber 28after the water supply at S14. If it is determined at S17 that thetemperature decreasing width in the water storage chamber 28 from thetemperature decrease is equal to or higher than 20° C., the controller34 estimates a predetermined amount of water is stored in the waterstorage chamber 28, determining that the water storage in the waterchamber 28 has been completed (S19). FIG. 10C shows an example of such acase.

Meanwhile, when it is determined at S17 that the temperature decreasingwidth from the temperature decrease is equal to or less than 20° C., thecontroller 34 determines if a number of water supply is 8 or more times(S18). More specifically, it is determined whether or not the number ofthe water supply by the water supply pump 41 is 8 or more after thewater supply starts at S14. When it is determined at S18 that the numberof the water supply is 8 or more, the controller 34 judges that asufficient amount of water has been supplied in the water storagechamber 28, determining that the water storage in the water storagechamber 28 has been completed.

If it is determined at S18 that the number of the water supply is lessthan 8 times, the process returns to S14 again to perform the watersupply to the water storage chamber 28.

Such a control flow is to repeat S14-S18 until any of the results ofS16-S18 is YES and it is determined that the water storage has beencompleted at S19. Thus, the intermittent water supply to the waterstorage chamber 28 will be performed.

In the first embodiment, the intermittent water supply is repeated, butsuch a case is not limiting. For example, the same amount of the watermay be supplied by lengthening the period of the single water supplywhile reducing the flow rate by the water supply pump 41.

Such water supply to the water storage chamber 28 increases the waterlevel to a level below the second steam generating heater 51 and thespaces between the fins 36 are filled with water. Heating in this stateusing the first steam generating heater 50 and the second steamgenerating heater 51 can heat the water in the water storage chamber 28either directly or via the fins 36, thereby evaporating the heated waterto generate steam. The steam generated in the water storage chamber 28passes through the steam spout port 45 and the steam passage 31 and isdischarged from the steam spout port 32 into the heating chamber 10. Thesteam discharged into the heating chamber 10 heats the inside of theheating chamber 10 and the food 11. In this event, if the food 11 isplaced on the food tray 9, which is in turn placed on the rails 12, theinside of the heating chamber 10 is partitioned by the food tray 9 andthus a space in the heating chamber 10 to be filled with steam isreduced, thus making it possible to efficiently heat only the space inwhich the food 11 is present.

If it is determined that the water storage is completed and the processproceeds to S19, 10-second masking time for determining water supply isprovided (S20). More specifically, a waiting time without performing thewater supply is provided for 10 seconds.

Then, the evaporation continues, the water levels of the water storagechamber 28 and drainage 43 are lowered, and the temperature of the waterstorage chamber 28 is increased. Next, it is determined whether or notthe temperature of the water storage chamber 28 is equal to or less than110° C. (S21). When it is determined at S21 that the temperature of thewater storage chamber 28 exceeds 110° C., the controller 34 operates thewater supply pump 41 for 1.5 seconds (S22). As a result, water of about9 ml is supplied into the water storage chamber 28. Then, the controlflow goes back to S20. The water supply decreases the temperature of thewater storage chamber 28. Next water supply will not be performed untilthe evaporation continues, the water level is lowered, and thetemperature is increased. Here, the water supply amount by the watersupply pump 41 is adjusted so that the water level in the water storagechamber 28 does not exceed the second steam generating heater 51. Inother words, the water level “h1” shown in FIG. 6, in which the waterstorage chamber thermistor 33 detects a temperature exceeding 110° C.for performing the water supply, is set below the center of the firststeam generating heater 50. In addition, the water level “h2” shown inFIG. 6 is set above the center of the first steam generating heater 50.Such a setting of the water levels can maintain the water level in thevicinity of the first steam generating heater 50 during the steamgeneration. Therefore, it can be controlled so that the water level inthe water storage chamber 28 does not fall below a certain level, andthe water level can be detected via the water storage chamber thermistor33 without using a water level sensor which detects the water leveldirectly. In the first embodiment, at the time of steam generation, thecontroller 34 controls the water supply such that the capacity (volumeor distance) of the water from the first steam generating heater 50 tothe water level is smaller than the capacity (volume or distance) of thewater from the first steam generating heater 50 to the bottom surface 37in the water storage chamber 28.

In the first embodiment, when the water level has come below the centerof the first steam generating heater 50, the water supply is performedto above the center of the first steam generating heater 50, but such acase is not limiting. For example, both the water levels “h1” and “h2”may be set under the center of the first steam generating heater 50 aslong as they are positioned in the vicinity of the first steamgenerating heater 50. Similarly, both the water levels “h1” and “h2” maybe set above the center of the first steam generating heater 50 as longas they are positioned in the vicinity of the first steam generatingheater 50. Thus, it will be sufficient if the water level can bemaintained in the vicinity of the first steam generating heater 50 atall times during steam generation.

Meanwhile, when temperature increasing of the water storage chamber 28does not stop even if the water supply instruction was issued to thewater supply pump 41, it is determined that the water in the watersupply tank 42 has run out, or the water supply pump 41 or the likebreaks down. If so determined, the steam heating is terminated to soundthe buzzer, and contents to prompt the water supply into the watersupply tank 29 is displayed on the touch panel 57 to notify the user.Alternatively, cooking may be continued without sounding the buzzer ifthe cooking menu has been selected, whose cooking performance is notgreatly influenced by the presence or absence of the steam heating.

If it is determined at S21 that the temperature of the water storagechamber 28 is equal to or less than 110° C., the process proceeds toS23. S23 is to determine if the steam heating time has ended, and if thesteam heating is canceled. If the result of S23 is NO, the process goesback to S21. Meanwhile, if the result of S23 is YES, energization of thefirst steam generating heater 50 and the second steam generating heater51 is stopped (OFF) (S24), and the cooking is finished (S25).

It should be noted that the threshold values of the temperature (forexample, 110° C., 20° C.) of the water storage chamber 28 used in theflow shown in FIG. 9, the operating time of the water supply pump (forexample, 1.5 seconds), and the water supply determination time (forexample, 5 seconds, 10 seconds) may be appropriately determined, as theywill vary greatly depending on the shape of the water storage chamber28, or the outputs of the first steam generating heater 50 and thesecond steam generating heater 51.

The steam generator 27 in the first embodiment includes a water storagechamber 28 which stores water therein, a heater (first steam generatingheater 50 or second steam generating heater 51) which heats inside thewater storage chamber 28 to generate steam, a water supply device (watersupply pump 41) which supplies the water storage chamber 28 with water,a steam spout port 32 which ejects steam generated in the water storagechamber 28 therethrough, a temperature detector (water storage chamberthermistor 33) which detects a temperature in the water storage chamber28, and a controller 34 which controls the heater and the water supplydevice. After the start of the heating by the heater, the controller 34determines if water storage is completed in the water storage chamber 28based on the temperature detected by the temperature detector. Thus, thesteam generator 27 uses the temperature detector which detects thetemperature in the water storage chamber 28 not using a water leveldetector which is likely to cause false detection, thereby generatingsteam while accurately detecting water amount in the water storagechamber 28 if a large amount of water is stored in the water storagechamber 28.

According to the steam generator 27 in the first embodiment, after thestart of heating the water storage chamber 28 by the heater, thecontroller 34 starts the water supply by the water supply device whenthe temperature of the water storage chamber 28 detected by thetemperature detector becomes equal to or higher than a firstpredetermined temperature (for example, 110° C.), and determines if thewater storage in the water storage chamber 28 is completed based on thetemperature in the water storage chamber 28 after the start of the watersupply. Such control is to start the water supply with estimating thatthe water amount in the water storage chamber 28 becomes small when thetemperature of the water storage chamber 28 becomes equal to or higherthan the first predetermined temperature. Thus, the steam generator 27can generate steam while accurately detecting the water amount in thewater storage chamber 28 using the temperature detector.

According to the steam generator 27 in the first embodiment, after thewater supply, the controller 34 determines that the water storage in thewater storage chamber 28 is completed when the temperature in the waterstorage chamber 28 becomes equal to or lower than a second predeterminedtemperature (for example, 110° C.). Such control is to determinecompletion of the water storage with estimating that the water storageamount is increased to a predetermined storage amount when thetemperature of the water storage chamber 28 becomes equal to or lowerthan the second predetermined temperature. Thus, the steam generator 27can generate steam while accurately detecting the water amount in thewater storage chamber 28 using the temperature detector. Also, the steamgenerator 27 can prevent overflow of the water from the water storagechamber 28 due to excess water supply or prevent slow steam generationdue to insufficient water supply.

According to the steam generator 27 in the first embodiment, thecontroller 34 operates the water supply pump to perform the water supplyuntil it is determined that the water storage has been completed whenthe temperature detected by the water storage chamber thermistor 33 isdecreased by equal to or more than a predetermined temperature widthfrom the maximum degree in which the temperature changes from increaseto decrease. That is, after the water supply by the water supply device,the controller 34 determines that the water storage in the water storagechamber 28 is completed when the temperature in the water storagechamber 28 is decreased by equal to or more than a first temperaturewidth (for example, 20° C.) from the start of the decrease. Such controlis to estimate that the water storage amount in the water storagechamber 28 becomes equal to or larger than a predetermined amount whenthe temperature in the water storage chamber 28 is decreased by equal toor more than the first temperature width (for example, 20° C.) from thestart of the decrease after the water supply, in particular, in a casewhere an initial water level in the water storage chamber 28 is low.Thus, the steam generator 27 can generate steam while accuratelydetecting the water amount in the water storage chamber 28 using thetemperature detector. Also, the steam generator 27 can prevent overflowof the water from the water storage chamber 28 due to excess watersupply or prevent slow steam generation due to insufficient watersupply.

According to the steam generator 27 in the first embodiment, thecontroller 34 operates the water supply pump to perform the water supplyuntil it is determined that the water storage has been completed whenthe temperature detected by the water storage chamber thermistor 33 ismaintained at a substantially constant temperature in a predeterminedperiod. That is, after the start of heating inside the water storagechamber 28 by the heater, the controller 34 determines that the waterstorage in the water storage chamber 28 has been completed when atemperature change of the water storage chamber 28 detected by thetemperature detector is within a second temperature width (for example,±1° C.) in a predetermined period (for example, 10 seconds), and thencontrols the water supply device not to supply the water. Such controlis to estimate that the water level in the water storage chamber 28 issufficiently high by the fact that the temperature change of the waterstorage chamber 28 detected by the temperature detector is within thepredetermined temperature width in the predetermined period after theheating. Thus, the steam generator 27 can generate steam whileaccurately detecting the water amount in the water storage chamber 28using the temperature detector. Also, the steam generator 27 can preventoverflow of the water from the water storage chamber 28 due to excesswater supply or prevent slow steam generation due to insufficient watersupply.

Also, the controller 34 controls the water supply device to supply thewater intermittently. Such control can control the water supply amountmore accurately.

According to the steam generator 27 in the first embodiment, thecontroller 34 operates the water supply pump 41 to perform the watersupply until it is determined that the water storage has been completedwhen a number of the water supply by the water supply pump 41 reaches apredetermined number. That is, the controller 34 determines that thewater storage in the water storage chamber 28 is completed when thenumber of the water supply by the water supply device reaches thepredetermined number (for example, 8 times). Such control can completewater storage with sufficient amount of water even if the water supplywas started when no water was initially stored in the water storagechamber 28. Also, overflow of the water from the water storage chamberdue to excess water supply can be prevented.

The steam generator 27 according to the first embodiment is providedwith a water storage chamber 28 which stores water therein, a firstheating portion (a first steam generating heater 50) which heats waterstored in the water storage chamber 28 to generate steam, a water supplydevice (a water supply pump 41) which supplies the water storage chamber28 with water, a controller 34 which controls water supply by the watersupply device, a steam spout port 32 which ejects steam generated in thewater storage chamber 28 therethrough, and a temperature detector (awater storage chamber thermistor 33) which detects the temperature inthe water storage chamber 28. Also, the water level in the water storagechamber 28 is calculated depending on the temperature detected by thetemperature detector and, at the time of steam generation, thecontroller 34 is configured to perform a water supply control of thewater supply device in such a manner that the water volume from thefirst heating portion to the water surface is smaller than the watervolume from the first heating portion to the bottom surface of the waterstorage chamber. Accordingly, water in the vicinity of the water surfacewithin the water storage chamber 28 can be intensively heated andevaporated by the first steam generating heater 50, thus making itpossible to quickly generate steam. For this reason, even if a largeamount of water is stored in the water storage chamber 28, a steamgenerator 27 operable to quickly generate steam at an early stage can beprovided. Also, boiling at a lower portion within the water storagechamber 28 can be suppressed by minimizing heating of water at the lowerportion within the water storage chamber 28. Although bubbles generatedby the boiling may grow into large bubbles while moving upward and thelarge bubbles may further move upward to the water surface andeventually burst, the suppression of boiling can reduce running-up ofboiling water due to such a bubble burst, thus making it possible toprevent the boiling water from spouting from the steam spout port 32.Bursting sounds of the bubbles can be also suppressed.

Also, the steam generator 27 according to the first embodiment isfurther provided with a second steam generating heater 51 disposed abovethe first steam generating heater 50, and an output of the first steamgenerating heater 50 is not less than that of the second steamgenerating heater 51. This can heat water adjacent to the water surfacewithin the water storage chamber 28 more efficiently, thereby generatingsteam quickly. Accordingly, even if a large amount of water is stored inthe water storage chamber 28, a steam generator 27 operable to quicklygenerate steam at an early stage can be provided.

Further, in the steam generator 27 according to the first embodiment,the distance between the first side surface 53 and the second sidesurface 54 facing each other within the water storage chamber 28 isincreased at a location below the first steam generating heater 50. Thiscan store a large amount of water in a lower portion (water storagechamber recess 28 a) of the water storage chamber 28 and, hence, theamount of water stored remains large even if evaporation progresses.Accordingly, scale condensation is unlikely to occur, thus making itpossible to quickly generate steam while suppressing scale deposition.For this reason, even if a large amount of water is stored in the waterstorage chamber 28, a steam generator 27 operable to quickly generatesteam at an early stage can be provided.

Also, the steam generator 27 according to the first embodiment isprovided with a water supply port 38 below the first steam generatingheater 50 within the water storage chamber 28 to allow the water supplydevice (water supply pump 41) to supply the water storage chamber 28with water. This configuration is to supply water to a low-temperaturelower portion of the water storage chamber 28, instead of supplyingwater to a location adjacent to the water surface having hightemperature in the vicinity of the first steam generating heater 50,which will result in temperature decreasing near the water surface.Accordingly, heated water is moved upward toward the first steamgenerating heater 50, thus making it possible to generate steamefficiently and quickly. That is, even if a large amount of water isstored in the water storage chamber 28, a steam generator 27 operable toquickly generate steam at an early stage can be provided.

Further, in the first embodiment, water is refilled to the full waterline 52, but steam heating can be performed with refilling water underthe full water line 52 as long as long-term steam heating is not needed.

Also, in the first embodiment, the water supply port 38 and the waterdischarge port 39 are provided at a lower portion of the water storagechamber 28. Accordingly, at the time of steam generation, the watersupply port 38 and the water discharge port 39 are submerged in waterand, hence, temperature rising at the water supply port 38 and the waterdischarge port 39 are both reduced, and it is accordingly unlikely thatscales adhere to the water supply port 38 and the water discharge port39. This can prevent the water supply port 38 and the water dischargeport 39 from being clogged with scales, which may prevent water supplyand water discharge, and to provide a highly-reliable steam generator 27capable of maintaining the steam generating performance even afterlong-term continuous use.

FIG. 11A is a first cross-sectional view of the steam generator 27according to the first embodiment, schematically depicting a waterdischarge process according to the siphon principle. FIG. 11B is asecond cross-sectional view of the steam generator 27 according to thefirst embodiment, schematically depicting the water discharge processaccording to the siphon principle. FIG. 11C is a third cross-sectionalview of the steam generator 27 according to the first embodiment,schematically depicting the water discharge process according to thesiphon principle. FIG. 11D is a fourth cross-sectional view of the steamgenerator 27 according to the first embodiment, schematically depictingthe water discharge process according to the siphon principle.

As shown in FIG. 11A, at the time of normal heating, water has beenstored in the water storage chamber 28 to a level (normal level H) belowthe second steam generating heater 51 as a result of water supply fromthe water supply pump 41, and also a water level in the water dischargepassage 43 has been increased. If no steam is generated in the waterstorage chamber 28, a water level in the water storage chamber 28 is thesame as the water level in the water discharge passage 43. In contrast,if steam is generated in the water storage chamber 28, the pressureinside the water storage chamber 28 will be increased to raise the waterlevel in the water discharge passage 43. In this case, the water levelin the water storage chamber 28 is not always the same as the waterlevel in the water discharge passage 43.

After having refilled the water supply tank 42 with water to a levelindicated by the full water line 52, a user selects a water dischargemode using the touch panel 57. When the start button of the operatingportion 58 is pushed, water supply is performed. Specifically, as shownin FIG. 11B, the water supply pump 41 is automatically driven for watersupply until the water level in the water storage chamber 28 reaches awater discharge passage upmost point 44 located above the water levelduring the normal heating. If the water level is raised to the waterdischarge passage upmost point 44, a difference “a” in height is createdbetween the water level in the water storage chamber 28 and the waterlevel in the water discharge passage 43. Then, as shown in FIG. 11C,scale-condensed water and precipitated scales in the water storagechamber 28 and the water discharge passage 43 flow toward the waterdischarge tank 47 through the water discharge port 39, the waterdischarge passage 43 and the water discharge passage outlet 46 accordingto the siphon principle.

When the difference “a” in height is created between the water level inthe water storage chamber 28 and the water level in the water dischargepassage 43, water discharge starts, but the water supply flow rate maybe less than the water discharge flow rate. In this case, even if watersupply is performed, the water level in the water storage chamber 28 isnot raised, and even if water supply is performed by the water supplypump 41 in an amount slightly greater than the amount of water supplyrequired for water discharge, no water overflows from the water storagechamber 28. Therefore, in the steam generator 27 according to the firstembodiment, the driving time of the water supply pump 41 is determined,in consideration of variations in operation of the water supply pump 41,so as to supply water in an amount slightly greater than the amount ofwater supply required for water discharge. Accordingly, in the steamgenerator 27 according to the first embodiment, a detector for detectingthe water level in the water storage chamber 28 at the time of waterdischarge can be omitted.

Finally, as shown in FIG. 11D, the water storage chamber 28 and thewater discharge passage 43 are emptied of water, and discharged water isstored in the water discharge tank 47. The water discharge tank 47 isremoved from the heating cooker 1 by a user, and then the user disposeof water stored in the water discharge tank 47. In the above-mentionedwater discharge process, water in the water supply passage 40 around thewater supply pump 41 located upstream and downstream of the water supplypump 41 is not discharged.

Adopting such a configuration of the water discharge passage 43 andperforming water supply to the water discharge passage upmost point 44can clean scales deposited in the water storage chamber 28. Thus, merelyperforming the water supply can perform the water discharge using thesiphon principle. Therefore, scales and scale-condensed water can bedischarged using a simple configuration. That is, a highly-reliable andinexpensive steam generator 27 capable of reducing a user's burden canbe provided.

In the steam generator 27 according to the first embodiment, waterdischarge is performed if the user has selected a water discharge mode,but the present invention is not limited to such a case. For example,water discharge may be automatically performed for each steam heatingafter setting water amount in the water supply tank 42 to maintainsufficient amount after cooking.

FIG. 12A is a first cross-sectional view of the steam generator 27according to the first embodiment, schematically depicting a waterdischarge process in the water supply passage 40. FIG. 12B is a secondcross-sectional view of the steam generator 27 according to the firstembodiment, schematically depicting the water discharge process in thewater supply passage 40. FIG. 12C is a third cross-sectional view of thesteam generator 27 according to the first embodiment, schematicallydepicting the water discharge process in the water supply passage 40.FIG. 12D is a fourth cross-sectional view of the steam generator 27according to the first embodiment, schematically depicting the waterdischarge process in the water supply passage 40.

After having refilled the water supply tank 42 with water to a levelindicated by the water discharge line 49, a user selects a water supplypassage discharge mode using the touch panel 57 and pushes the startbutton of the operating portion 58. Then, as shown in FIG. 12A, water inthe water supply tank 42 is supplied to the water storage chamber 28through the water supply passage 40 and the water supply port 38 by thewater supply pump 41.

Further, when water supply is continued, the water level of the waterstorage chamber 28 and the water discharge passage 43 reaches the waterdischarge passage upmost point 44 as shown in FIG. 12B. Because thewater supply tank 42 contains water of a volume only about 10 ml morethan the volume of the water storage chamber 28, the water supply tank42 becomes almost empty.

As shown in FIG. 12C, water is discharged toward the water dischargetank 47 through the water discharge port 39, the water discharge passage43 and the water discharge passage outlet 46 according to the siphonprinciple. Even when water is discharged to the water discharge tank 47in the above-described manner, the water supply pump 41 operatescontinuously. Then, the water supply tank 42 becomes empty by thecontinuous operation of the water supply pump 41. Therefore, the watersupply pump 41 supplies air to the water supply passage 40 instead ofwater. As a result, the water supply pump 41 pushes the water in thewater supply passage 40 into the water storage chamber 28 with the airso supplied to discharge water from the water discharge passage 43.Then, the water supply pump 41 stops after a predetermined period oftime.

Finally, as shown in FIG. 12D, the water pushed into the water storagechamber 28 joins the water to be discharged according to the siphonprinciple and then is discharged toward the water discharge tank 47.Consequently, the water supply tank 42, the water supply pump 41, thewater supply passage 40, the water storage chamber 28 and the waterdischarge passage 43 become empty.

Although in the first embodiment the water discharge line 49 is providedon the water supply tank 42, the touch panel 57 may display “100 ml”,which is required for water discharge, to prompt the user to refill thewater supply tank 42 with the water. Also, heating by the first steamgenerating heater 50 and the second steam generating heater 51 may beperformed together with the use of a cleaning agent such as citricsolution instead of water, thereby making it possible to easily removedirt such as scales or water stains in the water storage chamber 28 andto provide a cleaner steam generator 27.

As just described, water discharge by the siphon principle is performedby operating the water supply pump 41 to increase the water level to thewater discharge passage upmost point 44, with the water supply tank 42having a predetermined amount of water. Even while the water dischargeby the siphon principle is being performed, the water supply pump 41 isoperated to continue water supply. According to such a control, evenwhen the water supply tank 42 becomes empty of water, the water supplypump 41 feeds air instead of water into the water supply passage 40,thereby making it possible to push and discharge water remaining in thewater supply passage 40. The discharged water joins the water to bedischarged by the siphon principle and is discharged simultaneously.Therefore, water in the water supply passage 40 located upstream anddownstream of the water supply pump 41 and water in the water supplypump 41 can be discharged, which cannot be discharged by the siphonprinciple. That is, a steam generator 27 capable of performing waterdischarge at low costs can be provided.

As described above, the steam generator 27 according to the firstembodiment includes a water storage chamber 28 which stores watertherein, at least one heating portion (a first steam generating heater50) which heats water in the water storage chamber 28 to generate steam,a water supply device (a water supply pump 41) which supplies the waterstorage chamber 28 with water, a steam spout port 32 which spouts thesteam generated in the water storage chamber 28 therethrough, and aplurality of fins 36 positioned below the steam spout port 32 in asteam-generating direction and spaced from one another. Also, a firstdistance d1 between the plurality of fins 36 differs from a seconddistance d2 between an inner wall side surface 28A of the water storagechamber 28 and one of the fins 36 facing the wall side surface 28A. Thisconfiguration can increase contact area between the fins 36 and water,where the smaller distance of the first distance d1 and the seconddistance d2 is adopted, to increase the heat transfer efficiency. On theother hand, the longer distance allows scale pieces to fall off prior tocomplete clogging and, hence, the complete clogging is unlikely tooccur. Accordingly, steam can be always spouted from the steam spoutport 32 while increasing the heat transfer efficiency between the fins36 and water. That is, even if the pressure inside the steam generator27 increases, steam or water can be prevented from leaking from thewater storage chamber 28, thus making it possible to provide ahighly-reliable steam generator 27 capable of maintaining the steamgenerating performance even after long-term use.

Also, in the steam generator 27 according to the first embodiment, theheating portion is one or more heaters (a first steam generating heater50 and a second steam generating heater 51), and at least one of thefins 36 crosses the heater. This configuration allows heat in thevicinity of the first steam generating heater 50 and the second steamgenerating heater 51 both having a particularly high temperature totransfer via the fins 36 to water in the water storage chamber 28, whereheat is unlikely to transfer. Also, because the fins 36 increase thecontact area between the water storage chamber 28 and water toefficiently transfer heat to water, the temperature around the firststeam generating heater 50 and the second steam generating heater 51decreases, thereby making it possible to prevent scales, which arelikely to adhere with an increase in temperature, from adhering to thefirst steam generating heater 50 and the second steam generating heater51.

Further, in the steam generator 27 according to the first embodiment,the first distance d1 in the first range e1 within the water storagechamber 28 is smaller than the second distance d2 in the second rangese2. Because the temperatures of the steam generating heaters 50 and 51are higher in the centrally-located first range e1 than in the secondranges e2, the first distance d1 is set to be smaller than the seconddistance d2 so that the contact area with water is increased to furtherincrease the heat transfer efficiency. On the other hand, thetemperatures of the steam generating heaters 50 and 51 are low in thesecond ranges e2, so making the second distance d2 greater than thefirst distance d1 can reduce scale accumulation. Accordingly, steam canbe always spouted from the steam spout port 32 while increasing the heattransfer efficiency between the fins 36 and water. That is, even if thepressure inside the steam generator 27 increases, steam or water can beprevented from leaking from the water storage chamber 28, thus making itpossible to provide a highly-reliable steam generator 27 capable ofmaintaining the steam generating performance even after long-term use.

Although in the first embodiment the first distance d1 in the firstrange e1 has been described as being smaller than the second distance d2in the second ranges e2, the first distance d1 may be greater than thesecond distance d2.

Also, the steam generator 27 according to the first embodiment isprovided with a recess 30 a positioned in an inner wall of the waterstorage chamber cover 30 at a location facing the heating portion (firststeam generating heater 50). That is, the recess 30 a is provided in thewater storage chamber cover 30 at a location facing a water storagechamber protrusion 28 b of the water storage chamber 28. Thisconfiguration increases the inner volume between the water storagechamber protrusion 28 b and the recess 30 a of the water storage chambercover 30 in the vicinity of the first steam generating heater 50, towhich scales are likely to adhere particularly at high temperatures and,hence, the scales are unlikely to accumulate. Accordingly, steam can bealways spouted from the steam spout port 32 while increasing the heattransfer efficiency between the fins 36 and water. That is, even if thepressure inside the steam generator 27 increases, steam or water can beprevented from leaking from the water storage chamber 28, thus making itpossible to provide a highly-reliable steam generator 27 capable ofmaintaining the steam generating performance even after long-term use.

Also, the steam generator 27 according to the first embodiment isprovided with a water storage chamber 28 which stores water therein, aheating portion (a first steam generating heater 50) which heats waterstored in the water storage chamber 28 to generate steam, a water supplydevice (a water supply pump 41) which supplies the water storage chamber28 with water, a water discharge passage 43 which discharges waterthrough a water discharge port 39 provided in the water storage chamber28, a steam spout port 32 which spouts steam generated in the waterstorage chamber 28, and a rib 55 integrally formed with an inner wallsurface of the water storage chamber 28 so as to cross the inside of thewater storage chamber 28 and having a plurality of openings 59. Theopenings 59 in the rib 55 are smaller than the water discharge port 39.This configuration allows the rib 55 having the openings 59 to blockscales, thus making it possible to prevent the water discharge port 39from being clogged with scales, without using a separate filter or thelike. If the separate filter is used, the fixing position of the filterdepends when the filter is fixed by welding or the like, or if the waterstorage chamber 28 and the filter are made of different metals, acontact portion between them may become eroded to thereby create a gap.In such a case, the scales may pass through the gap and clog the waterdischarge port 39. On the other hand, in the first embodiment, the rib55 having the openings 59 smaller than the water discharge port 39 canblock the scales, thereby making it possible to prevent water dischargeimpossibility due to scale clogging. That is, a highly-reliable steamgenerator 27 capable of maintaining the steam generating performanceeven after long-term use can be provided.

Although in the first embodiment the openings 59 are formed by recesses55A defined in the rib 55, the present invention is not limited to sucha case, and the openings 59 may be formed as through-holes in the rib55. Also, the cross-sectional shape of the openings 59 in the rib 55 isnot limited to a rectangular shape and may be in the form of a round,ellipsoidal or polygonal shape other than the rectangular shape.

Also, in the steam generator 27 according to the first embodiment, theopenings 59 in the rib 55 are positioned below the heating portions (thefirst steam generating heater 50 and the second steam generating heater51). By this configuration, when scales fall off that have adhered to alocation adjacent to the first steam generating heater 50 and the secondsteam generating heater 51, to which the scales are likely to adhereparticularly at high temperatures, the openings 59 in the rib 55positioned below them can positively block the scales.

The steam generator 27 according to the first embodiment is alsoprovided with a controller 34 which controls the vertical position ofthe water surface within the water storage chamber 28. Also, theopenings 59 in the rib 55 are positioned below a lower limit of thevertical position of the water surface controlled by the controller 34at the time of steam generation. Because this configuration allows therib 55 having the openings 59 to be held in contact with water, atemperature rise of the rib 55 is suppressed, thereby making it possibleto prevent scales from adhering to a flow passage formed by the rib 55and prevent water discharge impossibility due to clogging of the waterdischarge port 39 with the scales.

The steam generator 27 according to the first embodiment is providedwith a plurality of mutually-spaced fins 36 positioned below the steamspout port 32 and extending along a steam-generating direction. The rib55 crosses the fins 36 and the openings 59 in the rib 55 are positionedbetween the fins 36. This configuration allows the plurality of fins 36to divide scales adhering to the water storage chamber 28 to therebyprevent the scales from growing big. Accordingly, even if the scalesfall off, it is possible to prevent water discharge impossibility due toclogging of the openings 59 and the water discharge port inlet 39A withthe scales. Also, the water storage chamber 28 is partitioned by theplurality of fins 36 to isolate each of the plurality of openings 59from each other, thus making it possible to prevent the openings 59 frombeing simultaneously clogged with big scales.

Further, in the steam generator 27 according to the first embodiment,the fins 36 adjacent to the rib 55 have respective distal end side edges36B generally held in contact with a second side surface 54. By thisconfiguration, scales are unlikely to pass through possible gaps betweenthe distal end side edges 36B of the fins 36 and the second side surface54, thus making it possible to prevent water discharge impossibility dueto clogging of the water discharge port inlet 39A with the scales.Accordingly, a highly-reliable steam generator 27 capable of maintainingthe steam generating performance even after long-term use can beprovided.

Also, the steam generator 27 according to the first embodiment includesa water storage chamber 28 which stores water therein, at least oneheating portion (a first steam generating heater 50 or a second steamgenerating heater 51) which heats water in the water storage chamber 28to generate steam, a water supply device (for example, a water supplypump 41) which supplies the water storage chamber 28 with water, and aplurality of fins 36 positioned in the water storage chamber 28. Thewater storage chamber 28 has a steam spout port 32 defined therein tospout the steam generated by the heating portion therethrough. Theplurality of fins 36 are positioned below the steam spout port 32 alonga steam-generating direction and spaced from one another so as to crossthe heating portion. This configuration allows heat in the vicinity ofthe heating portion having a particularly high temperature to transfervia the fins 36 to water in the water storage chamber 28, in which heatis unlikely to transfer. Also, because the fins 36 act to increase thecontact area between the water storage chamber 28 and water, heat fromthe heating portion can be efficiently transferred to the water. Thisreduces the temperature at a location where the water storage chamber 28is held in contact with the water and also reduces the number of largebubbles that may be created at high-temperature portions. It isaccordingly possible to reduce running-up of boiling water that may becaused by a phenomenon in which the large bubbles rise to the watersurface and eventually burst, thus making it possible to prevent theboiling water from spouting from the steam spout port 32. Burstingsounds of the bubbles can be also suppressed. Also, a reduction in thenumber of the large bubbles can suppress bursting sounds of the bubbles.Further, a reduction in temperature of the contact portion between thewater storage chamber 28 and the water can suppress adhesion of scalesthat is likely to occur with an increase in temperature.

In the steam generator 27 according to the first embodiment, the waterstorage chamber 28 is finely partitioned by the fins 36. This canphysically reduce the sizes of the bubbles during boiling, therebyfurther reducing the generation of the large bubbles. Also, in the steamgenerator 27 according to the first embodiment, the fins 36 are arrangedalong the steam-generating direction. This configuration does notinterrupt steam flows, thus making it possible to increase the amountand flow rate of steam.

Further, in the steam generator 27 according to the first embodiment,the cross-sectional areas of spaces formed by the water storage chamber28 and the fins 36 in a plane perpendicular to the steam-generatingdirection are not smaller than the cross-sectional area of the steamspout port 32. This leads to a reduction in cross-sectional area of asteam passage, thereby reducing a pressure loss of the steam passage tosuppress a reduction in the amount of steam, as compared with a casewhere the cross-sectional area increases. That is, by reducingrunning-up of the boiling water, while suppressing the reduction in theamount of steam, the boiling water can be prevented from ejecting fromthe steam spout port 32, and the bursting sounds of the babbles can bereduced.

In the steam generator 27 according to the first embodiment, the fins 36extend from a first side surface 53 of the water storage chamber 28, anddistal ends of the fins 36 are spaced from a second side surface 54facing the first side surface 53. Thus, water can flow between the fins36 and the second side surface 54, thereby increasing the contact areabetween the water storage chamber 28 and the water. This facilitateswater convection to uniform the temperature distribution of the water inthe water storage chamber 28. Accordingly, the generation of largebubbles can be reduced to thereby reduce running-up of the boilingwater, thus making it possible to prevent the boiling water fromejecting from the steam spout port 32 and reduce the bursting sounds ofthe babbles.

Also, in the steam generator 20 according to the first embodiment, theheating portions (the first steam generating heater 50 and the secondsteam generating heater 51) are respectively provided above and belowthe water surface in the water storage chamber 28 during heating. Thus,even when the bubbles generated during boiling burst at the watersurface and run up, the heating portion arranged above the water surfaceheats the bubbles and changes them into steam, thereby making itpossible to prevent the boiling water from ejecting from the steam spoutport 32.

Also, the steam generator 27 according to the first embodiment includesa water storage chamber 28 which stores water therein, heating portionswhich heat water in the water storage chamber 28 to generate steam, anda water supply device which supplies the water storage chamber 28 withwater. An inner wall of the water storage chamber 28 has a steam spoutport 32 defined therein to spout steam generated by the heating portiontherethrough. Two heating portions are respectively provided above andbelow the water surface in the water storage chamber 28 at the time ofheating. Thus, even when the bubbles generated during boiling burst atthe water surface and run up, the heating portion arranged above thewater surface heats the bubbles and changes them into steam, therebymaking it possible to prevent the boiling water from ejecting from thesteam spout port 32.

Also, the steam generator 27 according to the first embodiment includesa water storage chamber 28 which stores water therein, a first steamgenerating heater 50 and a second steam generating heater 51 which heatwater in the water storage chamber 28 to generate steam, a water supplypump 41 which supplies water through a water supply port 38 and a watersupply passage 40 defined in the water storage chamber 28, a steam spoutport 32 which spouts the steam generated in the water storage chamber 28therethrough, and a water storage chamber thermistor 33 which detectsthe temperature of the water storage chamber 28. After the start ofoperation, a controller 34 starts heating the water storage chamber 28using the first steam generating heater 50 and the second steamgenerating heater 51 and determines an initial amount of water supplydepending on a temperature increasing rate of the water storage chamber28 detected by the water chamber thermistor 33 for a given time. Basedon such a determination of the initial amount of water supply, water isstored in the water storage chamber 28 for steam generation, therebymaking it possible to prevent the water from overflowing from the waterstorage chamber 28 without using any water level detector and alsoprevent the water storage chamber 28 from being heated in an emptystate. It is accordingly possible to prevent failure of the first steamgenerating heater 50 and the second steam generating heater 51 due toexcessive heating and also prevent a reduction in the steam generatingefficiency. That is, a highly-reliable and safe steam generator 27 canbe provided.

In the steam generator 27 according to the first embodiment, if atemperature rise of the water storage chamber 28 detected by the waterstorage chamber thermistor 33 is not greater than 50° C. in 30 seconds(A3 in FIG. 10), water supply by the water supply pump 41 is notperformed. In contrast, if the temperature rise of the water storagechamber 28 exceeds 50° C. in 30 seconds (A2 in FIG. 10), the watersupply chamber 28 is supplied with about 20 ml of water using the watersupply pump 41. That is, if the temperature rise of the water storagechamber 28 is not greater than 50° C. in 30 seconds, it is estimatedthat the water level in the water storage chamber 28 is high, and watersupply is not performed. This can prevent water from overflowing fromthe water storage chamber 28. Also, if the temperature rise of the waterstorage chamber 28 exceeds 50° C. in 30 seconds, it is estimated thatthe water level in the water storage chamber 28 is low, and apredetermined amount of water supply is performed. Thus, the temperatureof the water storage chamber 28 is decreased to thereby prevent no-waterburning of the water storage chamber 28. It is accordingly possible toprevent failure of the first steam generating heater 50 and the secondsteam generating heater 51 due to excessive heating and also prevent areduction in the steam generating efficiency. That is, a highly-reliableand safe steam generator 27 can be provided.

Further, in the steam generator 27 according to the first embodiment,the amount of water supply when the temperature rise of the waterstorage chamber 28 exceeds 60° C. in 30 seconds (A1 in FIG. 10) is setto be greater than the amount of water supply when the temperature riseof the water storage chamber 28 exceeds 50° C. and is not greater than60° C. (A2 in FIG. 10). That is, if the temperature increasing rate ofthe water storage chamber 28 is relatively high, it is estimated thatthe water level of the water storage chamber 28 is low, and a largeramount of water supply is performed compared to the amount of watersupply when the temperature increasing rate is relatively low. Thus, thetemperature of the water storage chamber 28 is decreased to therebyprevent water from overflowing from the water storage chamber 28.Further, the predetermined amount of water supply can prevent no-waterburning of the water storage chamber 28, and it is accordingly possibleto prevent failure of the first steam generating heater 50 and thesecond steam generating heater 51 due to excessive heating and alsoprevent a reduction in the steam generating efficiency. That is, ahighly-reliable and safe steam generator 27 can be provided.

Also, in the steam generator 27 according to the first embodiment, awater discharge passage 43 is provided so as to extend from a waterdischarge port 39 defined in the water storage chamber 28 via a locationabove the water surface in the water storage chamber 28 during normalheating. Water supply by the water supply pump 41 raises the water levelin the water discharge passage 43 to a level above the water dischargepassage upmost point 44, thus making it possible to discharge waterstored in the water storage chamber 28 through the water discharge port39 and the water discharge passage 43 by the siphon principle.Accordingly, even if a large amount of water supply is performed inspite of a high water level of the water storage chamber 28, no waterdischarge is allowed until the water level in the water dischargepassage 43 reaches the water discharge passage upmost point 44.Accordingly, false water discharge can be prevented.

In the steam generator 27 according to the first embodiment, the waterdischarge passage 43 is made of silicone. Because silicone forms a poorbond with scales, the scales are less likely to adhere to the waterdischarge passage 43. Accordingly, when water is discharged by thesiphon principle, the scales can be easily and reliably discharged fromthe water discharge passage 43. As a result, a highly-reliable steamgenerator 27 capable of maintaining the steam generating performanceeven after long-term continuous use can be provided.

Further, the use of an elastic body for the water discharge passage 43can connect the water discharge port 39 to the water discharge passage43 without using a separate member such as a tube. Accordingly, waterleakage or the like can be avoided, which may be caused by an increasein number of component parts, thus making it possible to provide ahighly-reliable and inexpensive steam generator 27.

Also, although in the first embodiment one water storage chamberthermistor 33 is used to readily estimate the water level in the waterstorage chamber 28, the present invention is not limited to such a caseand, for example, a plurality of water storage chamber thermistors 33may be provided in the water storage chamber 28. Alternatively, thewater level in the water storage chamber 28 or the water dischargepassage 43 may be detected by using a water level sensor that directlydetects the water level in the water storage chamber 28, thereby makingit possible to control the amount of water supply more precisely. Thatis, the steam generator may include the following component parts: awater storage chamber 28 which stores water therein, a first heatingportion (a first steam generating heater 50) which heats water in thewater storage chamber 28 to generate steam, a water supply device (awater supply pump 41) which supplies the water storage chamber 28 withwater, a controller 34 which controls water supply by the water supplydevice, a steam spout port 32 which spouts the steam generated in thewater storage chamber 28 therethrough, and a water level detector (awater level sensor which directly detects the water level, or a waterstorage chamber thermistor 33) which directly or indirectly detects thewater level in the water storage chamber 28. At the time of steamgeneration, the controller 34 controls water supply in such a mannerthat the water volume from the first heating portion to the water levelbecomes smaller than the water volume from the first heating portion toa bottom surface of the water storage chamber depending on the waterlevel detected by the water level detector.

Further, although in the first embodiment the water supply tank 42 andthe water discharge tank 47 have been described as being formedseparately, they may be formed unitarily to prevent a user fromforgetting to attach the water discharge tank 47, thereby making itpossible to prevent discharged water from spilling on a floor. Also, byunitarily forming the water supply tank 42 and the water discharge tank47, the water discharge tank 47 can be removed at the time of pouringwater into the water supply tank 42, thus making it possible to avoidforgetting to dispose of water, which may be caused by forgetting toremove the water discharge tank 47. It is also possible to prevent thewater discharge tank 47 from becoming full of water and prevent waterfrom subsequently overflowing therefrom.

Also, the steam generator 27 according to the first embodiment isprovided with a water discharge tank detecting device (not shown). Whena user forgets to set the water discharge tank 47 or has removed ithalfway, the water discharge tank detecting device acts to stopoperation of the first steam generating heater 50, the second steamgenerating heater 51 and the water supply pump 41, thereby making itpossible to prevent discharged water from spilling on the floor.

Also, in the steam generator 27 according to the first embodiment, aninner bottom surface 37 of the water storage chamber 28 is tapered so asto incline downward toward the water discharge port 39, and the watersupply port 38 and the water discharge port 39 are oriented in oppositedirections at respective positions opposed to each other. Thisconfiguration allows a water flow from the water supply port 38 toeasily push and flow small scales, which have accumulated on the innerbottom surface 37 of the water storage chamber 28, toward the waterdischarge port 39. It is accordingly possible to reduce the amount ofremaining water at the time of water discharge on the siphon principle.

In the first embodiment, the procedure can be immediately transferred toa water discharge process after completion of steam heating, becausewater supply performed for water discharge according to the syphonprinciple can lower the water temperature in the water storage chamber28 at the same time. However, the present invention is not limited tosuch a case, and after completion of steam heating, water discharge maybe performed after water in the water storage chamber 28 has beennaturally cooled for a while until the water temperature in the waterstorage chamber 28 reaches a predetermined temperature or lower. This isbecause the solubility of calcium carbonate as a kind of scalesincreases with a reduction in temperature, and a user does not burnhimself or herself even if the user touches the water just discharged.It is preferable that the temperature of the discharged water is lower,but the time required for natural cooling increases with a reduction intemperature of the discharged water. Therefore, the temperature of thedischarged water should be adequately determined considering a balancewith the cooling time.

The heating cooker 1 according to the first embodiment of the presentinvention can be operated in each of a microwave heating mode, an ovenheating mode, a grill heating mode and a steam heating mode, but heatingcan be manually or automatically performed by combining the respectiveheating modes.

The steam generator according to the present invention is applicable, asa cooking device to use steam, to various applications such as microwaveovens, microwave ovens equipped with an oven function, electrical ovens,rice cookers, thawing devices for business use or the like.

Although the present invention has been fully described by way of apreferred embodiment with reference to the accompanying drawings, it isto be noted here that various changes and modifications will be apparentto those skilled in the art. Therefore, unless such changes andmodifications otherwise depart from the scope of the present inventionas set forth in the appended claims, they should be construed as beingincluded therein.

What is claimed is:
 1. A steam generator comprising: a water storagechamber which stores water therein, a heater configured to apply heatinside the water storage chamber to generate steam, a water supplydevice configured to supply the water storage chamber with water, asteam spout port configured to eject steam generated in the waterstorage chamber therethrough, a temperature detector configured todetect a temperature in the water storage chamber, and a controllerconfigured to control the heater and the water supply device, whereinafter a start of heating by the heater, the controller is configured to:start to supply the water by the water supply device if determining thatthe temperature of the water storage chamber detected by the temperaturedetector becomes higher than a first predetermined temperature, andwherein the temperature in the water storage chamber decreases from thesupply of water to the water storage chamber, the controller is furtherconfigured to determine whether the detected temperature after the watersupply becomes equal to or lower than a second predeterminedtemperature, and to control the water supply device to stop the watersupply when it is determined that the detected temperature becomes equalto or lower than the second predetermined temperature, when it isdetermined that the detected temperature after the water supply does notbecome equal to or lower than the second predetermined temperature, thecontroller is further configured to determine whether the detectedtemperature after the water supply is decreased by equal to or more thana predetermined temperature value from a start of the temperaturedecrease, and to control the water supply device to stop the watersupply when it is determined that the detected temperature after thewater supply is decreased by equal to or more than the predeterminedtemperature value, thereby regulating an amount of water storage in thewater storage chamber without the use of a water level sensor.
 2. Thesteam generator according to claim 1, wherein after the start of theheating by the heater and before determining if the detected temperaturebecomes higher than the first predetermined temperature, the controlleris further configured to determine if a temperature change of the waterstorage chamber detected by the temperature detector is within apredetermined temperature range, and to control the water supply deviceto stop the water supply when it is determined that the temperaturechange is within the predetermined temperature range, when it isdetermined that the temperature change is not within the predeterminedtemperature range, the controller is configured to determine if thedetected temperature becomes higher than the first predeterminedtemperature.
 3. The steam generator according to claim 1, wherein thecontroller is further configured to: control the water supply device tosupply the water intermittently, and determine if a number ofintermittent water supply cycles of water supplied by the water supplydevice reaches a predetermined number, and then control the water supplydevice to continue the water supply when the number of intermittentwater supply cycles of water supplied by the water supply device doesnot reach the predetermined number and to stop the water supply when thenumber of intermittent water supply cycles of water supplied by thewater supply device reaches the predetermined number.
 4. A heatingcooker provided with the steam generator according to claim
 1. 5. Thesteam generator according to claim 3, wherein the controller is furtherconfigured to determine whether the number of intermittent water supplycycles of water supplied by the water supply device reaches thepredetermined number when it is determined that the detectedtemperature, after the water supply, is not decreased by equal to ormore than the predetermined temperature value.